Zovirax (acyclovir) vs. Valtrex (valacyclovir)

What is acyclovir? What is Valtrex?

Acyclovir is a type of antiviral drug called a synthetic nucleoside analogue used to treat cold sores, genital herpes, herpes zoster (shingles), varicella zoster (chickenpox), herpes simplex encephalitis, and mucocutaneous herpes simplex virus infection. Acyclovir works by interfering with viral replication against the herpes viruses, including herpes simplex 1 and 2 (cold sores and genital herpes), varicella-zoster (shingles and chickenpox), and Epstein-Barr virus (mononucleosis). Viruses take over living cells and reproduce themselves, often at the expense of the host cell. Acyclovir is converted to an active form by the virus itself, and the virus then uses the active form of acyclovir rather than the nucleoside it normally uses to manufacture DNA, a critical component of viral replication. Incorporation of active acyclovir into new viral DNA stops the production of the DNA. Virally infected cells absorb more acyclovir than normal cells and convert more of it to the active form, which prolongs its antiviral activity.

Valtrex (valacyclovir) is an antiviral drug active against the herpes viruses used to treat infections with shingles (herpes zoster), genital herpes (herpes simplex genitalis), and cold sores (herpes labialis). Valtrex is a nucleoside analog that mimics a building block of DNA. It stops the spread of herpes virus in the body by preventing the replication of viral DNA that is necessary for viruses to multiply. Other nucleoside analogs include acyclovir (Zovirax), and famciclovir (Famvir). Valacyclovir is y a “prodrug,” in is not active itself but it is converted to acyclovir in the body, and it is the acyclovir that is active against the viruses. Valacyclovir is active against the same viruses as acyclovir, but valacyclovir has a longer duration of action than acyclovir and can be taken fewer times each day.

QUESTION

Condoms are the best protection from sexually transmitted diseases (STDs). See Answer

What are the side effects of acyclovir and Valtrex?

Acyclovir

The most common side effects are

Other reported side effects include:

Valtrex

The side effect profile of Valtrex is similar to that of acyclovir (Zovirax).

Common side effects are:

Other important side effects are:

More serious side effects include central nervous system side effects which are more likely to happen in the elderly, for example:

Latest Sexual Health News

Daily Health News

Trending on MedicineNet

What is the dosage of acyclovir vs. Valtrex?

Acyclovir

Acyclovir may be taken with or without food.

  • Adult oral doses for treating genital herpes are 200 mg every 4 hours (5 times daily) for 7-10 days or 400 mg three times daily for 5-10 days.
  • Herpes Zoster (shingles) is treated with 800 mg every 4 hours (5 times daily) for 7 to 10 days.
  • The dose for treating chicken pox is 800 mg 4 times daily. The usual adult intravenous dose is 5-10 mg/kg every 8 hours for 7-10 days.

Valtrex

  • Valtrex may be taken with or without food.
  • In people with kidney disease, doses need to be reduced.
  • For the treatment of herpes zoster (shingles), the usual dose is 1 gm. three times a day for 7 days. Treatment should begin at the first symptom and is most effective if started within 48 hours of the onset of rash.
  • The dose for chickenpox is 20 mg/kg 3 times daily for 5 days (maximum dose is 1000 mg 3 times daily) and treatment should start at the earliest sign or symptom.
  • For the treatment of an initial episode of genital herpes, the usual dose is 1 gram (1000 mg) twice daily for 10 days. For the treatment of recurrent genital herpes, the usual dose is 500 mg twice daily for 3 days. For best results, treatment should be initiated within 12 hours of the start of symptoms.
  • The dose for cold sores is 2000 mg (2 grams) every 12 hours for 1 day.

SLIDESHOW

Erectile Dysfunction (ED) Causes and Treatment See Slideshow

What drugs interact with acyclovir and Valtrex?

Acyclovir

Acyclovir may be taken with or without food.

  • Adult oral doses for treating genital herpes are 200 mg every 4 hours (5 times daily) for 7-10 days or 400 mg three times daily for 5-10 days.
  • Herpes Zoster (shingles) is treated with 800 mg every 4 hours (5 times daily) for 7 to 10 days.
  • The dose for treating chicken pox is 800 mg 4 times daily. The usual adult intravenous dose is 5-10 mg/kg every 8 hours for 7-10 days.

Valtrex

Probenecid (Benemid) and cimetidine (Tagamet) may reduce the kidney’s clearance of Valtrex, leading to higher concentrations in the blood. This may lead to side effects of Valtrex.

Are acyclovir and Valtrex safe to take while pregnant or breastfeeding?

Acyclovir

There are no adequate studies of acyclovir in pregnant women. In a patient registry of women who used acyclovir during the first trimester, the rate of birth defects was similar to the rate of birth defects in the general population.

Acyclovir is excreted in breast milk, and a significant amount may be transferred to the infant.

Valtrex

  • Valtrex showed no effects on the fetus in animal studies; however, there has been no adequate evaluation of valacyclovir or (acyclovir) in pregnant women. The incidence of birth defects in women taking acyclovir is about the same as in the general population. Valtrex should only be used during pregnancy when the benefits to the mother outweigh risks to the fetus.
  • It is not known whether Valtrex is excreted into breast milk. It is known, however, that among women taking acyclovir, concentrations of acyclovir in breast milk are about four times higher than in the mother’s blood. The safety of valacyclovir in breastfeeding infants has not been established. Methods other than breastfeeding should be considered if valacyclovir must be taken while nursing.

Subscribe to MedicineNet’s General Health Newsletter

By clicking Submit, I agree to the MedicineNet’s Terms & Conditions & Privacy Policy and understand that I may opt out of MedicineNet’s subscriptions at any time.

Medically Reviewed on 7/26/2019

References

REFERENCE:

FDA Prescribing Information